Azeotropic distillation of hydro-carbon oils



May 29, 1945. K. H. ENGEL 2,376,870

AZEOTROPIC D ISTILLATION 0F HYDROCARBON OILS f l 4 Filed mmm 2a, 1941 lNvENToR /fafrl wfy Enya! ATTORNEY Patented May 29, 1945 f AzEoTRoPIo nrs'rnLArloN oF mailtocAan'oN oms 1 Karl Henry Engel, West Englewood, N. .1., a'ssignor, by mesne assignments, to Allied Chemical & Dye Corporation, a corporation of New York Application March 28, 1941, Serial No. 385,623

Claims.

This invention relates to a process for recovering volatile aromatic hydrocarbons from hydrocarbon mixtures containing them together with like-boiling, non-aromatic hydrocarbons.

More particularly, it relates to the separation from admixture with volatile aromatic hydrocarbons of like-boiling, non-aromatic hydrocarbons.

by a two-step azeotropic distillation, in the first stepVV of which a highly effective but difficulty recoverable azeotropic agent is provided, and in the second step of which a less effective but more `easily recoverable azeotropic agent is provided.

Numerous hydrocarbon oils are known which contain volatile aromatic hydrocarbons, such as benzene, toluene and the xylenes, singly or mixed, together with like-boiling,non-aromatic hydrocarbons. For example, catalytic treatment of a suitable petroleum fraction in the presence of hydrogen gives an oil consisting chiefly of hydrocarbons of both aromatic and non-aromatic char-y acter. For example, by such a process one may obtain an oil containing about toluene, 20% other aromatic 4hydrocarbons (including benzene and xylenes) Aand the remainder substantially paraflin and naphthene hydrocarbons. Gasoline fractions obtained by the distillation of certain types of petroleum frequently contain substantial proportions of'benzene, toluene or xylene, depending upon the boiling range of the gasoline fraction, vtogether with non-aromatic hydrocarbons. Oils of petroleum origin having a considerable drocarbons which, when recovered, are accompanied by similar difliculty separable constituents.

By fractional distillation of these oilscontaining aromatic hydrocarbons, fractions relatively high in aromatic content may be obtained. These aromatic fractions, however, willz still contain substantial amounts of the other constituents of the oil having boiling points in the neighborhood of the boiling point of aromatic hydrocarbons or forming mixtures of constant boiling point in the range of temperatures at which the aromatic hydrocarbon distills from the oil. The separation of aromatic hydrocarbons from materials distilling from the oil fraction at temperatures substantially higher or lower than the aromatic hydrocarbon does not present any great technical difficulties. The recovery of a pure aromatic hydrocarbon froman oil fraction containing it, such i. as those referred to j above, involves the'problem content of aromatics may be treated by well i known selective solvent processes to produce fractions rich in aromatics; for example, extraction of suitable fractions of such petroleum oils with sulfur dioxide may-yield fractions of high .toluene content. In such cases the toluene is accompanied by non-aromatic oils which may be largely parafllnic, naphthenic or oleflnic in character. A considerable portion of these oils cannot be completely separated from the toluene by .direct fractional distillation because of the closeness of their boiling points to that of toluene or because they form' constant boiling mixtures with toluene. Furthermore, while ordinarily benzene, toluene or xylenes are readily separable by d irect fractional distillation from light oils pro-- duced by the vgasification of coal, in some cases the aromatic hydrocarbons are accompanied by diillculty separable non-aromatic oils of the saine general character as described, owing to carbonization conditions, type of coal used -or other special circumstances. Also synthetic hydrocarbon gas mixtures produced by various catalytic processes may contain toluene or other aromatic hyof separating the aromatic from the like-boiling, non-aromatic hydrocarbons; i. e., from those hydrocarbons which by direct fractional distillation processes as commonly operated for the fractional distillation of oils, distill from the'aromatic-oil fraction within the same temperature range as the aromatic hydrocarbon distills therefrom.

Processes have been developed whereby an aro- `matic hydrocarbon of any desired purity upto substantially may be successfully recovered from oils separate from the like-boilng, nonV f aromatic hydrocarbons. These processes involve azeotropic distillation of the aromatic oil fraction with fractionation of the vapors of aromatic hydrocarbon and other hydrocarbons in the presence of a material forming lov/boiling a'zeotropes with the like-boiling, non-aromatic hydrocarbons. Although the aromatic and like-boiling, non-aromatic hydrocarbons distill from mixtures con.

' with the aromatic hydrocarbons, the azeotropes of the non-aromatic and aromatic hydrocarbons have sufficiently different boiling temperatures to permit them to be separated ,by fractionation.

Accordingly, by azeotropic distillation of an aro- I matic oilfraction in the presence of azeotropic agents such as those mentioned, the aromatic hydrocarbons may be separated from like-boiling, non-aromatic hydrocarbons, the latter being distilled of! as azeotropes. Since materials con- .j tained in the oil fractions distilling therefrom below or above the aromatic hydrocarbon distilla-A tion range may be readily separated from the aromatic hydrocarbon by ordinary fractional disl tillation, thisprocess employing azeotropic distillation provides a method whereby the diiliculty i separable like-boiling, non-aromatic hydrocarl obtained.

It is an object of this invention to provide a l particularly effective process forv azeotropically separating volatile aromatic hydrocarbons from like-boiling, non-aromatic hydrocarbons; it is l bons may be separated from 'the aromatic hydro- -3 carbon and an aromatic product of desired purity especially applicable to the separation and recovery of aromatic hydrocarbonsy boiling below 150 C., and particularly hydrocarbons of the benzene series such as benzene, vtoluenel and i xylene. The economical commercial use *ofA an azeotropic distillation process for the treatnient l of aromatic hydrocarbon fractions depends upon 1 numerous factors.

the sharpness with which the aromatic hydrocarbon is separated from the non-aromatic hy- Of great importance are: (1)

drocarbons and the proportion of aromatic hydrocarbon contained in the oil fraction subjected tothe azeotropic distillation which is recoverable l as an aromaticy product of the desired purity, l v and (2) theprovision of suitable methods for separating the azeotropicl agent from the hydrocarbon distillate. `Usually it is important also to 1 recover the azeotropic agent from the distillate for reuse in the treatment of additional aromatic fraction. Azeotropic agents are known which acy complish a reasonably good separation of the t relatively` volatile aromatic hydrocarbons from like-boiling,I non-aromatic hydrocarbons and which may be recovered from the distillate for reuse in the process. I have discovered; howpresent invention is, accordingly, directed to a` process giving improved results by employing suitable pairs of azeotropic agents in the distillation of aromatichydrocarbon fractions as com pared with theiresults obtained using but a single azeotropic agent'. Theinvention permits of using an azeotropic agent which is relatively effective for the separation of the aromatic and nonaromatic hydrocarbons and thus obtaining al high recovery of the aromatic hydrocarbon purified from the non-aromatic hydrocarbons. The use of this highly-effective azeotropic agent perlmits'of carrying out the azeotropic distillation in columns of relatively simple construction or per-` mitsof rapidly carrying out the distillation, etc.

The invention further provides for use in conjunction with this azeotropic agent, which is effective for separating the aromatic and non-` aromatic hydrocarbons but is dimculty separable from the distilled hydrocarbons, of a less effective` azeotropic agent which separates the former i agent from the hydrocarbons and returns it for reuse, while being itself readily separable from` benefits of readily separating 'the distilled hydrocarbons from both azeotropic agents.

My invention comprises azeptropically matic hydrocarbons and like-boiling, non-aromatic hydrocarbons, employing two different azeotropic agents, one in each step of the distillation. The two azeotropic agents, which I will refer to as agent A and agent B, have the following characteristics:

Agent A (used in vthe second step of the distillain hydrocarbons and rich in agentfA. Agent B (used in the first step of the distillation) (1) More effectively than agent A separates e the non-aromatic hydrocarbons of the aromatic fraction from the aromatic hydrocarbonin distilling the aromatic fraction.` By this I meanthat when a given oil containing aromatic and like-boiling, non-aromatic hydrocarbons is distilled under comparable conditions with-agent B and also with agent A until substantially all the like-boiling, non-aromatic hydrocarbons have been distilled over, when lagent B is used the distillate contains a lower ratio of aromatic to ever, that in distilling an aromaticoil fraction, by using two azeotropic agents which are suitably related to eachother, the yield of aromatic hythe hydrocarbon distillate. I thus obtain the i benetsderived from `using the more effective agent for the separation of the aromatic and .l l non-aromatic hydrocarbons in addition to the non-aromatic hydrocarbons than when agent A y is used. I l

(2) Is not readily separable from the distillate; e. g., it forms azeotropes with the likeboiling, non-aromatic hydrocarbonsv to be distilled from the aromatic fraction which on cool` ingfdo not separate into two phases containing respectively a high and a low proportion 'of agent B, as compared with the proportions of agent A in the respective phases formed by cooling the azeotropes of agent A and those non-aromatic hydrocarbons.

(3) Agent B and any azeotropes it may form with A alone and with A together with hydrocarbons in the aromatic oil fraction have higher boiling points than agent A and than-` the azeo-l tropes of agent A with the hydrocarbons in the aromatic oil fraction. y

Azeotropic agents differ among themselves in carrying capacity for non-aromatic hydrocabcns, i. e., the ratio of non-aromatic hydrocarbons to agent in theirV azeotropes. `Agents forming azeotropes inwhich this ratio is high are preferably used. For agents with a reasonable carrying capacity for the non-aromatic hydrocarbons, the important factor controlling the effectiveness with, which aromaticand like-boiling, non-aromatic hydrocarbons are separated, is the difference between the boiling points of the azeotrope of the aromatic hydrocarbon, if such an azeotrope is formed, and the azeotropes of the likeboiling, non-aromatic hydrocarbons. If no aro-k matic azeotrope is formed, the dierence between the boiling points of the aromatic hydrocarbon itself and of the non-aromatic azeotropes is con-'- trolling. Thewider the spread between these distilling in two steps ari-oil fraction containing aroto be distilled from the oil fraction. The amount y boiling points, the more eiectively the aromatic and like-boiling, vnon-aromatic hydrocarbons `are separable by distilling with the azeotropic agent.

The aromatic fraction is iirst fractionally distilled in the presence of agent B to take over as distillate the like-boiling, non-aromatic hydrocarbons in the form of their azeotropes with agent B, leaving behind an aromatic hydrocarbon residue relatively free of these non-aromatic hydrocarbons. The distillate thus obtained is fractionally distilled in the presence of agent A. Agent A dlsplaces agent B from the distillate and carries over as distillate, inthe form of lower boiling azeotropes with agent Al the hydrocarbons in the distillate of the rst step. Agent B is left as the residue of the second distillation step and is returned for reuse in the iirst step. Agent A is recovered from the second distillate for reuse, preferably by cooling the condensed distillate to separate it into two liquid phases, a hydrocarbon phase low in or substantially free from agent A and a second phase low in hydrocarbons and high in agent A. The latter phase is returned to the second distillation step for reuse therein of its content of agent A. The other phase, the hydrocarbon phase, is withdrawn from the process.

If desired, this phase may be further treated to `v recover therefrom any of agent A' it may contain. Moreover, it is sometimes of advantage to separate agent A from the oils accompanying it as it leaves the column by other than the means just mentioned; e. g., by extraction of agent A from such oil by a solvent; separation of agent A from such solvent by any desired means, and return to the column of the recovered agent A with or without part of the accompanying oil.

The two distillation steps of the process of my invention may be carried out either as batch or as continuously operating procedures. The two distillations may be carried out in series in separate distillation columns or other suitable fractional distillation apparatus, with the distillate from the first step being condensed before being introduced into the apparatus in which the second distillation step is. carried out. I have found, however, that the two distillation steps may be effectively carried out, for example, in a single distillation column, without intermediate condensation of the distillate from the first step, vand this mode of operation represents a particularly eilicient method of practicing my invention. In thus operating, the vapor distillate from the rst distillation step passes directly, without condensation into the second distillation step and'supplies the heat required for that distillation. The liquid agent B, with associated non-aromatic hydrocarbons, ows directly from'the second distillation step to serve as reilux in the first step. VThis mode of combining the twosteps gives important economies in the apparatus and heating and cooling requirements as compared with operating the two distillation steps separately with intermediate condensation of the distillate from the iirst step.

In employing a' single distillation column suiii-l cient of agent A is maintained in the column so that it is'present only in the upper portion, e. g.,

one-iifth to one-tenth of the column, during the distillation of the oil fraction toseparate the likeboiling, non-aromatic from the aromatic hydrocarbons. While the amount of agent A in the column at any given time is thus limited, in the course of distilling a given amount of aromatic oil fraction an amount of agent A is supplied to the column suiiicient to carry over the hydrocarbons of agent B present in a single distillation column used for both Steps ofthe distilmlation is S'lcient for agent B to be present only in a lower 4 portion of the column, e. g., the lower four-fifthsA to a region or zone where agent A is present. In the upper portion of the column agent A sepa-V rates the hydrocarbons from agent B, the latter returning for reuse in the lower portion of the column and agent A carrying over the hydrocar-y bons from the top of the column as a distillate of the azeotropes of these hydrocarbons with agent A.

The relationship between the portions of the column in which'agents A andv B are maintained is related to the work accomplished by these two agents. Thus, the separation of an aromatic hydrocarbon from the like-boiling, non-aromatic hydrocarbons accomplished by agent B is relatively diflicult, since the spread between the boiling points of the azeotropes of B with an aromatic hydrocarbon and with like-boiling, nonaromatic hydrocarbons is usually relatively small. Accordingly, the tower or column space required for rectifying the vapors of the aromatic oil fraction and agent B to eiect a good separation between the aromatic and like-boiling, non-aro- Amatic hydrocarbons is relatively large. yother hand, by proper choice of pairs of agents A and B, an agent A may be used which forms azeotropes with the hydrocarbons to be distilled from the oil fraction havingwidely different boiling points from the boiling point of the azeo.

tropes of agent B with those same hydrocarbons. Accordingly, a much smaller tower or column volume is required for adequate rectification of the vapors of the B' azeotropes in the presence ofof the aromatic Vfrom the like-boiling, non-aro-v matic hydrocarbons in the presence ofv agent B. It is generally not desirable that agent B be present in large excess over that required for this separation of the aromatic ,and like-boiling, nonaromatic hydrocarbons. On the other hand, my

-process may be carried out employing larger quantities of agent B, so that the' aromatic residue of the distillation contains substantial proportions of this agent. Such a mode of operation, however, requires removalof agent B from the residue before a pure aromatic product 1s obtained and is particularly undesirable' in a continuously operating process where it is desired to'contlnuously withdraw from the bottom of the distillation column a pure aromaticv hydrocarbon either as liquid residue or as a vapor drawn from the column ata point where the vapors therein are the aromatic hydrocarbon from which the like-boiling, vnon-aromatic hydrocarbons and agent B have been separated.

Under vthese conditions On the i 1.4 l The above description of the conditions in a 'distillation column operating to carry out the which obtain during the time the column is operlating to separate effectively lthe aromatic and the like-boiling, non-aromatic hydrocarbons in the distillation of an aromatic oil fraction. In starting and at the end of a distillation, as more `particularly illustrated in connection with the specific examples to be described, these conditions do not necessarily exist. in the column. Thus, in a batch procedure the materials (i. e., the aromatic oil fraction, agent A and agent B) l all may be initially placed in a boiler attached to a rectification column. When distillation of such a mixture is started the vapors rst passing upwardly through `the column will consist largely l of azeotropes of agent A accompanied by smaller proportions of azeotropes of agent B. Since, however, as pointed out above, the amount of azeotropic agent A is sufficient to fill only an upper 1 portion of the column at a given moment during the distillation, a state of equilibrium will process of this invention is of the conditionsv quickly establish itself in which agent A is presv 1 ent only in the upper portion of the column and agentB is present in the lower portion of the column. 1

I have discovered that as agent B p-dioxane or crotonaldehyde is particularly efficacious is distilling toluene oils to separate the toluene from l' like-boiling,y non-aromatic hydrocarbons. I have Q further discovered that with either p-dioxane or crotonaldehyde, methanol is peculiarly suit- Q able for use as agent A. Aqueousethanol may be used as agent Awith crotonaldehyde used as agent B; Methanol forms no azeotropes with i p-dioxane or crotonaldehyde, and aqueous ethanol forms no azeotropes with crotonaldehyde.,

with or without the non-aromatic hydrocarbons. I The methanol and aqueous ethanol form azeotropes with the non-aromatic hydrocarbons4 i which, when cooled, separate into two phases; a l hydrocarbon oil phase low in methanol or ethal nol and a second phase low in hydrocarbons and rich in methanol or ethanol which may be re- 1 turned to the azeotropic distillation step for reuse therein o f the methanol or ethanol.

` For th distillation of a xylene fraction water may be used'as agent A with the methyl ether 1 of ethylene glycol as agent B. Themethyl ether of ethylene glycol accomplishes a separation of xylene (ortho, metaand para-xylenes) from i like-boiling, lnon-aromatichydrocarbons. The water accomplishes a separation of the methyl ether of ethylene glycol from its azeotropes with the non-aromatic hydrocarbons and carries overA the latter as azeotropes which, when cooled and condensed, separatey into two layers; a water layer and a hydrocarbon layer;

1 My invention will be more particularly described and illustrated by the following examples for the azeotropic distillation of aromatic l g oil fractions.

column. A vapor line from the top of the rectication column leads toa condenser for. cooling and liquefying the vapors. The condenser is con--v nected to a decantation vessel into which the condensed liquid is passed and from',l which thetop and bottom liquid phases separating out in the vessel may be separately withdrawn. Suitable provision is made for returning part of the distillate to the column as reflux. `Glass or chemical stoneware are suitable materials of construction for this apparatus.' Any material which is inert towards the liquids being treated may be used.

'I'he toluene fraction treated by the process of 'specific dispersion method described in Industrial and Engineering Chemistry, Analytical edition,

vol. 1l, page 614, November 15, 1939.

A mixture of 100 parts of this toluene fraction, 50 parts of p-dioxane and 8 parts of anhydrous methanol (parts'by volume) was introduced into the still of the apparatus described above.-

The liquid mixture was boiled and the vapors passed into the rectication column. The vapors from the top of the column were condensed in the cooler and the condensate passed to the decantation vessel in which the two liquid phases formed by the cool condensate 4were stratified. The bottom layer and a portion of the top layer were introduced into the top of the rectification column to provide reiiux for this column. Conditions were quickly established such that the upper portion of the rectification column, the cooler and the decantation vessel contained methanol and its azeotropes with the hydrocarbons distilled over. column andthe still contained dioxane and its azeotropes with the hydrocarbons passing from the still into the rectification column,

The azeotrope of dioxane and toluene boils at about 101.6 C. The azeotropes of the dioxane and like-boiling, non-aromatic hydrocarbons present in the toluene fraction boil in the range of about 96.6 to about 98.9'C. (There is thus a relatively narrow temperature spread between the boiling points of the toluene and non-aromatic azeotropes of 2.7 to 5 C. Accordingly, arelatively high degree of fractionation of the vapors ot these azeotropes in the rst distillation step of my process is required for their separation.

In the second distillation step of the process of this example, the dioxane hydrocarbon azeotropes taken oi as distillate in the first step are distilled in the presence of methanol. Since the methanol azeotropes with the hydrocarbons present boil at temperatures lower than the dioxane azeotropes. the hydrocarbonsv are carried over as distillatel by the methanol leaving the dioxane behind as residue. This dioxane flowing downwardly in the rectication column is returned to and reused in the iirst distillation step. The Adioxane azeotropes with the non-aromatic hydrofrom the 'still to the bottom of the rectication carbons removed from the toluene fraction boil, as pointed out above, at about 96.6 to about 98.9 C. 'Ihe methanol azeotropes with these hydrocarbons boil at about 61 C. to about 63 C.

Due to this ,wide spread between these boiling points, a relatively small degree of fractionation of the vapors in the second distillation step of my process sufllces 1 to carry over the methanolhydrocarbon azeotropes and leave behind the dioxane as a residue for return to the rst distillation step.

Distillation of the above toluene fraction by The bottom portion of the rectiilcation the process of this example started with the temperature of the vaporsat the top of the fractionation column at, substantially 61 C. The

condensed vapors separated into two liquid phases which were Withdrawn from the decalntation vessel. The vbottom phase rich in methanol and a part of the top phase were continuously returned as reflux tothe top of the column while the remainder of the top hydrocarbon oil phase was withdrawn from the process. As the distillation proceeded the temperature of the vapors at the top of the column gradually increased to vslightly above 63 C. At this temperature the condensate drawn from the vapor cooler ceased to separate into two phases. A part of the single phase condensate was continuously returned as reflux to the fractionationcolumn while the remainder. was taken oil' and collected separately from the hydrocarbon oil'phase obtained from the condensate during the initial stage of the distillation, As the distillation proceeded, the temperature of the vapors at the top of the column rose rapidly to 100 C. to 102 C. and remained there for a short time before again rising to 110.2 C.y

During the initial stage of the distillation, when the vapor temperatures were below 63 C., the amount of toluene in the oil phase withdrawn from the decantation vessel remained low;

i. e., this oil phase contained only about 3% toluene. It contained some methanol but mainlyA consisted of the like-boiling, non-aromatic hydrocarbons, amounting to about 90% of the nonaromatic hydrocarbons in the original toluene fraction. During the second stage of the distillation, when the temperatures at the top of the rectification column rose to 100 to 102 C. and then to 110.2 C., the ratio of toluene to other hydrocarbons in the distillate rose until the hydrocarbons Awere all toluene; i. e., the oil layer which formed upon washing thevdistillate with Water was substantially 100% toluene. During this stage of the distillation the methanol and dioxane were distilled over with the last of the non-aromatic hydrocarbons of the toluene fraction, leaving in the still and rectiiication column a residue of the distillation which was substantially 100% toluene and contained'80% of the toluene present in the toluene fraction initially supplied to the still. I n addition, toluene of the same quality, amounting to 12% of the toluene present in the initial toluene fraction, was recovered from a portion of the distillates which contained pure toluene and dioxane by washing with water to remove the dioxane. Thus, a total of 92% of the toluene present in the initial toluene fraction was recovered as substantially 100% toluene. By discontinuing the distillation at this point the toluene residue may be withdrawn as the toluene product of the distillation process. It may be given a conventional purification treat- 'ment to produce toluene of highest purity. Instead of stopping the distillation when the toluene residue has been substantially completely freed from the' like-boiling, non-aromatic hydrocar bons. the distillation may be continued' and the toluen'.` taken oii as distillate.

The oil fraction withdrawn from the decanta-` tion vessel during the iirst stage of this distillation contains seme methanol which may be recovered for reuse if desired. 'The distillate taken ofi during the second stage of the distillation conrains dioxane and particularly during the initial period. of this second stage methanol may comev over in the distillate. The last distillates con- 5 taining dioxane substantially consist of pure toluene-dioxane azeotrope. From these distillates, as pointed out in the preceding paragraph, an additional quantity of pure toluene maybe isolated. In the fractionation herein described, a somewhat greater quantity o1' dioxane was employed than was required for eiective removal of the non-aromatic hydrocarbons. A smaller quantity could be' used, the amount largely depending on the nature of the original oil fraction and on the capacity of the rectification column for holding liquid and vapors when operating under equilibrium'conditions. The amount to be used is independent of the size of the charge. The single phase distillate may all or in part be added to a new/.batch of toluene fraction to be distilled by the process and the methanol andy dioxane contained inthis distillate thus reused in the subsequent distillation of additional.

toluene fraction.

Example 2.--In place of p-dioxane, crotonaldehyde may be employed with methanol in distilling the toluene fraction by the process of Ex' ample 2. A mixture of 100 parts of the toluene fraction of Example l, parts of commercial -crotonaldehyde (a material having a boiling range 'of 82 to 108' C. and containing 90% crotonaldehyde) and 8 parts methanol (parts by volume) is introduced into the still of the .apparatus used in carrying out the process of Example l and distillation carried out as in that process. The distillation starts withthe vapors at the top of the fractionation column at a temperature of about 61 C. As in the case of the process of Example 1, the distillation takes place in two stages. During the iirst stage, with vapor temperatures up to about 62.5 C., the cooledV distillate separates into two liquid layers, a bottom layer rich in methanol which is returned as reiiux from'the decantation vessel to the rectiiication column and a top oil layer which is in part returned as'reiiux and in partvwithdr'awn from the process. This is followed by a stage of operation at higher temperatures up to about 102.8 C., during which a distillate which doesnot separate into two liquid phases is obtained containing rst methanol-hydrocarbons and then crotonaldehyde-hydrocarbon mixtures. When thel hydrocarbons coming over as distillate are substantially all toluene, i. e., when vthe distillation residue contains toluene substantiallycom'- pletely separated from the like-boiling, nonaromatic hydrocarbons which is indicated by the y treating a petroleum distillate in the presencek of 'I'he liquid mixture was distilled and the vapors 1 toluene.

hydrogen. This` oil' fraction contained .74%

A mixture of parts of the toluene fraction, 18 parts of crotonaldehyde (the material used in Example 2) and 5 parts vof 94% aqueous ethanol (parts being given byvolumel Awas introduced into a still communicating with a rectication column provided with a condenser for the vapors leaving the top of the column and a separator for separating two liquid `phases of the condensate.

rectified in this apparatus. Distillation was started with the temperature oi' the vapors at the top of the still at substantially 73 C. and, as `the distillation continued, the temperature mounted to 77.2 C. During'this stage of the distillation the crotonaldehyde occupied the lower portion of Y the fractionation column and the aqueous ethanol the upper portion. Non-aromatic hydrocarbons contained. in the oil fraction were carried over from the top of the fractionation column with a small proportion-of toluene as azeotropes with the aqueous ethanol which, when cooled and condensed, separated into two liquid layers. The bottom layer, rich in aqueous ethanol, was continuously returned as reilux to the top of the.

rectification column. The top hydrocarbon oil layer was in part returned as reux to the rectiiication column and in part withdrawn yand washed with water to remove the ethanol contained therein. Y Y A's the distillation was rising temperatures of the vapors leaving thetop further continued with carbons and carried those hydrocarbons over as azeotropes with ythe water which, upon cooling and condensation, separated into the two, liquid phases. I

As the distillation proceeded non-aromatic hydrocarbons became exhausted from the residue inr the still. The distillation'temperature, measured at the top of the rectification column, rose and the -condensed distillate, which at first formed two liquid phases, changed to a single phase liquid. When the temperature had risen to about 117 C.

- all of the water which had been supplied to the still had been taken over in the distillate and Y withdrawn. The temperature then continued to of the column, the condensed distillates formed h a single liquid phase. A part of the condensed i distillate was continuously returned as reux to the column and the remaining part taken oil' as overhead product and washed with water to` recover the hydrocarbons contained therein separate from the azeotropic agents. As the distillation proceeded, the amount of toluenecar- 'ried over in the distillate increased. When the voil recovered by washing the distillate with water contained 99.3 toluene and all the ethanol and crotonaldehyde had been carried over in theldistillates, the distillation was discontinued. Thev residue left in the still was substantially 100%- toluene vand contained about 78% of the toluene content of-jthe oil fraction initially supplied to the still/By recovering the ethanol and croton- Ealdehyl'lecarried over in the distillates, these materials may be reused' for the distillation of an` additional batch of toluene fraction.

Example 4.-The process of this example-was employed for the distillation of a petroleum fraction boiling in the range 125 C. to150 C. containing about 60% xylenes.

150 parts of this xylene oil fraction, 25 parts of ethylene glycol monomethyl ether (a commercial product boiling in the raige 118 C. to 126 C. and marketed under the name` Methyl Cellosolve") and 1.5 parts of water (all parts givenv rise to 129 C. with the xylene content of the hyi drocarbon oil in the distillate increasing to substantially 100%. The distillation was continued until the vapor temperature rose to 140.2? C. During these latter stages of the distillation, whenv the condensed distillate formed a single phase liquid, this condensate was divided, a portion bein'g returned as reflux to the, rectification column and another portion withdrawn. During the last stage, when the distillation temperatures were rising from 129 C. to 140.2 C., the distillate taken oif was recovered 4separate from the preceding distillate and was washed with water to recover its xylene content. The residue left in the still was also washed withwater. 'I'he xylene Y temperatures in the range 129 recovered from the final distillate (with vapor and that recovered asresidue from the still was 1 combined as a 99-l00% Xylene product containing about 70% of the xyl'enevcontent of the original oil fraction introduced to the still. l

I have heretofore referred to a conventional final purification treatment of the toluene product of the distillation process of this invention which contains toluene separated from like-boil- 40 ing, non-aromatic hydrocarbons. The art is familiar with such final treatments which involve washing toluene with concentrated sulfuric acid in'parts by volumel were introduced into a still communicating with a rectification column, a condenser for the distillate and a separator for separating the two phases of the condensed distillate. The `materials were distilled and the vapors rectified in this apparatus. Distillation started with the vapor temperature at the top of the still at about 91 C. and, as the distillation proceeded, this temperaturejgradually increased to 100 C. and finally to about 110 C. During I'he process of this invention is not limited to l the use as agent A of -a material forming with the hydrocarbons distilled from the aromatic oil frac.

v'tion a condensate which separates into two liquid this stage of the distillation the condensed distilv lates separated into two liquid phases. The bottom layer, principally consisting of water, was

,continuously returned as reflux to the top'of th'e column. 'I'he top hydrocarbon oil phase was in part returned as reflux and in part withdrawn.

l During'this stage of 'the distillation the ethylene glycol methylether was inthe lower portion of the fractionation column where it acted to separate the xylenes from the like-boiling, non-aromatic hydrocarbons' and carried` the latter in the form 'of azeotropes into the upper portion of the column. The water in the upper portion of the column "displace'most of the ethylene glycol methyl ether from its azeotropes with the hydrolayers, whereby agent A is readily separable from hydrocarbons distilled from the oil fraction in the l.form of their azeotropes. As pointed out above,

the invention comprises employing as agent`A a material which is more readily separable than agent B from the hydrocarbons of the distillate, whatever the particular method for separating agent A from the hydrocarbons may be. For example, methanol may be employed as agent A and vthe condensed single phase distillate treated lwith a small amount of water to separate the methanol as aqueous. methanol from the hydrocarbons in the distillate. Anhydrous methanol may be recovered from the aqueous methanol by distillation before returning the methanol for reuse as agent A. Such a process would 'be advantageous where the separationof agent B from hydrocar- C. t0 140.2 C.)

When the distillation is car-..

ically the procedure of this invention when carried out for the continuous distillation of an aromatic oil in a single rectification column provided with a heater.

In the drawing, the numeral l designates a rectification column containing a packing material such as saddle packing. 'I'he bottom of the column is provided with a heater 2. A liquid inlet pipe 3 serves for introducing liquid feed to the middle portion of the column. Withdrawal pipes 4 and 5 may be used for withdrawing liquid residue from the'bottom of column I or as a side stream from the bottom portion of the column. From the top of column I a vapor draw-ofi pipe leads to a condenser l. A pipe 8 leads from condenser 'I to a decanter 9. Pipe I0 leads from the top of decanter 9 and pipe II connects the decanter 9 with the top of column I for passage to the column of a lower liquid layer formed in the decanter. A pipe I2 serves to introduce azeotropic agent A through pipe II into the top of column I. A pipe I3 is provided tor returning. as desired, liquid from the top layer in decanter 9 to pipe I I and thence into the top of column I.

In starting operations employing the apparatus described above for carrying out the process of thisinvention for the recovery of an aromatic hydrocarbon from an oil containing it together with like-boiling, non-'aromatic hydrocarbons, specifically from a toluene fraction, 'the aromatic oil together with azeotropic agent B is led into column I through pipe 3. Azeotropic agent A is fed into the column through pipes I2 and II. The liquid flowing to the-bottom of the column is heated and distilled and the vapors from the top of the column taken of to condenser 1. Condensate flowing to decanter 9 is returned through pipes II and I3 to the top of the column. f

Agent B which, in the case of a toluene fraction may be p-dioxane, tends to be concentrated in the lower portion of rectification column I; Agent A,y which may be methanol in distilling a toluene fraction, tends to be concentrated in thetop of column I, in the vapors going over to condenser land in decanter 9, and in the liquid in the bottom layer in decanter 9 which is returned to the top of column I. The toluene tends tov become concentrated in the bottom of rectification column I while the like-boiling, non-aromatic'` hydrocarbons become vconcentrated in the top of rectification column I and are carried over in the distillate from the top of the column.. Owing to these tendencies of the respective` materials introduced into rectification column I, by controlling the amounts of agents A and B introduced to the column an equilibrium condition of operation will quickly be established in the packed section of the rectification column.

- Agent B will be present in the lower portion of tive length of the rectification column (i. e., the

length of the column containing the packing material) The feeding of agent B to the column is so yregulated as to maintain agent B in this lower section of the column but not to permit it to be Apresent in the top of the column. The top section of the column, e. g., the top one-fifth or one-tenth of the column (indicated in the drawing by the bracket designated agent A) contains agent A. There will be a short section of the column in which both agents A and B will be present as indicated in" the figure by the overlapping of the two brackets.

,The feed of agent A will be so regulated that this agent' will always be' present in the top portion of rectication column I and the vapors distilled over from the top of the column will contain the azeotropes of agent A with'the nonaromatic hydrocarbons in the oil fed to the column. In decanter l9 the mixture of agent A (c. methanol) and hydrocarbons distilled over, is separated into two liquid phases. The lower phase, rich in methanol, and any desired portion of the top phase is returned to the top of 'rectification column I-to provide a suitable volume of reflux for the column and to reuse the methanol asA agent Ain the distillation f the oil fed to the column. All or a portion of the top phase. rich in hydrocarbons fandv low in methanol, is withdrawn through pipe I0 for treatment as deaired.

As the distillation is continuously carried out,

once equilibrium conditions have been established as described above, the feed of fresh agent 'A i v(e. g., methanol) from pipe I2 to the top of reci system in starting operations for this agent to be present in the lower portion of column I, as described above, any additional amount of agent B introduced into the rectification column is only that required to make up for incidental losses of agent B from the system.

The presence in rectification column I of both agents Aand B establishes in that column two zones in which selective separation of materials being distilled in the apparatus takes place. The

zone occupied by agent B'serves to allow the passage downwardly through the column of the aromaticd hydrocarbon, e. g., toluene, while preventing the like-boiling, non-aromatic hydrocar-bons accompanying lthe toluene. These latter yhydrocarbons are kept by agen-t B in the Lipper portion of the rectification column. The zone occupied by agent A serves to retain` agent B in the lower portion of the column while the likeboiling, non-aromatic hydrocarbons are picked.

up by agent A and carried out in the' distillate from the top of the column. Agent A is readiy recoverable fro-m'this distillate for.l reuse'in the rectification column while agent B is retained in the column where it operates to separate 'effectively,v the like-boiling, non-aromatic hydrocarbons from the aromatic hydrocarbon. The latter flows to the bottom of rectification column I relatively free from like-boiling, non-aromatic hydrocarbons and is withdrawn through pipe 4 or pipe 5 as desired.

I claim: 1. The process for the treatment of an oil frac- ,tion containing a volatile aromatic hydrocarbon and a mixture of like-boiling, non-aromatic hydrocarbons which comprises fractionally distillate azeotropes' of said like-boiling, non-aromatic hydrocarbons withl agent B and leaving a residue enriched in said aromatic hydrocarbon, then'fractiona'lly distilling said distillate in the presence of an azeotropic agent A and thereby taking oil as distillate said like-boiling, non-aromatic hydrocarbons as azeotropes withv agent A 'and leaving agent B in an residue ofthe distillation, agent A being a polar organic compound which forms with said like-boiling, non-aromatic hydrocarbons. azetropes Vhaving lower boiling points lthan the azeotropes of agent B with said like-boiling, non-aromatic hydrocarbons and forms with the hydrocarbons distilled with A from said oil fraction'a mixture from which agent A is more readily separable than agent Bffrom the hydrocarbons distilled from said oil fractionwith agent B, and said agent B being a material from the group consisting of water and polar organic compounds which form lower boiling azeotropes with said like-boiling, non-aromatic hydrocarbons, `and said agent B being (1) more eiective than agent A for separating from the aromatic hydrocarbon the like-boiling,v non-aromatic hydrocarbons of said oil fraction and (2) less readily separable than agent A from the hydrocarbons distilled from said oil fraction with agentsB and A respectively, and (3) agent B and any azeotropes it may form with agent A alone and with A together with hydrocarbons in said oil fraction have higher boiling points than agent A and of agent A, and (3) agent B and any azeotropes it may form with agent' A alone and with A together with hydrocarbons in said oil vfraction have higher boiling points than agent A and the 5 azeotropesrof A with the hydrocarbons in said oil fraction, and in distilling said oil fraction returning said residue containing agent B to the aforedescribed distillation of said oil fraction in the presence of agent B, and returning the aforeboiling, non-aromatic hydrocarbons with agent B and leaving a residue enriched in toluene, thenv fractionally distilling said distillate in the presence of an azeotropic agent A and 'thereby taking oi as ldistillate said like-boiling, non-aromatic hydrocarbons as azeotropes ywith agent A and leaving agent B in a residue of the distillation', both of said agents -forming low boiling azeotropes with said like-boiling, non-aromatic hydrocarbons, agent A being a material which forms with said like-boiling, non-aromatic hydrothe azeotropes of A with the hydrocarbons in said oil fraction.

2. The process for the treatment of yan oil fraction containing a .volatile aromatic hydrocarbon -boiling below 150` C. and a mixture of like-boiling, non-aromatic hydrocarbons which comprises fractionally distilling said oil fraction in the pres.. ence of an azeotropic agent B and thereby taking oir as distillate azeotropes of said like-boiling, non-aromatic hydrocarbons with agent Band leaving a .residue enriched in said aromatic hydrocarbon, then fractionally distilling saiddistillate in the presence of an azeotropic agent A forms with said like-boiling, non-aromatic hydrocarbons azeotropes which separate intotwo liquid phases when the azeotropes are cooled, one

phase a hydrocarbon'oil phase low in agent A anda second phase low in hydrocarbons and rich in agent A, and said agent B being a material which (1) is more effective than agent A for separating from the aromatic hydrocarbon the likeboiling, non-aromatic hydrocarbons of said oil fraction, (2) forms azeotropes with said nonaromatic hydrocarbons which, when the azeoctropes are cooled, form a liquid containing` the hydrocarbons and a high proportion -of agent B as comparedwith the proportion of agent A in the aforesaid hydrocarbon oil phase and, `if ja second phase is formed, such-second phase' contains a small4 proportion ofl agent B as compared with the proportion of agent A in the second Y phase formed by coolingthe aforesaid azeotropes carbons azeotropes having lower boiling points than the azeotropes of agentB with said likeboiling, non-aromatic hydrocarbons and forms with said like-boiling, non-aromatic hydrocarbons azeotropes which separateinto two liquid phases when the azeotropes are cooled, one phase a hydrocarbon oil phase low in agent A and a second phase low in hydrocarbons and rich in agent A, and said agent B being a material which (1) is more effective than agent A for separating from the toluene andy like-boiling, non-aromatic hydrocarbons of said toluene fraction, (2)

l forms azeotropes with said non-aromatic hydro-l' carbons which, whenthe azeotropes are cooled, form a liquid,containing the hydrocarbons'and a high proportion of agent B as compared with the `proportion of agent A in the aforedescribed hydrocarbon oil phase and, if a second phase is J formed, suchsecond phase contains'a small proportion of agent B as compared-With the proportion of agent A in the second phase formed by cooling the aforesaid azeotropes of agent A, and (3) agent B and any azeotropes it may form with agent -A alone and with A together with hydrocarbons in'said oil fraction have higher boiling points than agent -A and the azeotropes of A withthe hydrocarbons in said oil fraction, and

in distilling said toluene fraction returning said residue containing agent B tothe aforedescribed distillation of said oil fraction in the presence of agent B, and returning the aforedescribed liquid l phase low in hydrocarbons and rich in agent A into contact with the distillate from said distillation of said `oil fraction lin.v the presence of agent B.

4. The process for the treatment of an oil frac- 'tion containing toluene and a mixture of likeboiling, non-aromatic hydrocarbons which comprises fractionally distilling. said oil .fraction in the presence of p-dioxane and thereby taking off yas distillate azeotropes of said like-boiling, nonaromatic hydrocarbons with p-dioxane and leaving a residue enriched in toluene, then fractionally distilling said distillate in the presence otls'lulcient methanol to carry over as distillate dehyde.

said like-boiling, non-aromatic hydrocarbons as azeotropes with the methanol. thereby leaving pdioxane in a residue of the distillation and returning said residue containing p-dioxane to the aforedescribed distillation of said oil fraction in the presence of p-dioxane.

5. The process for the treatment. of an oil fraction containing toluene and a mixture of likeboiling, non-aromatic hydrocarbons which com,- prises fractionally distilling said oil fraction in the presence of p-dioxane and thereby taking offas distillate vapors azeotropes of said like-boiling, non-aromatic hydrocarbons with p-dioxane and leaving a residue enriched in toluene, then fractionally distilling said distillate vapors in the presence of methanol and thereby taking voi'f as distillate said like-boiling, non-aromatic hydrocarbons asazeotropes with methanol and leavp-dioxane in a residue of the distillation, returning said residue containing p-dioxane to the aforedescribed distillation of said oil fraction in the presence of p-dioxane, cooling the distillate containing said like-boiling, non-aromatic hydrocarbons as azeotropes with methanol and thereby separating the distillate into two liquid phases and returning the liquid phase'thus obtained which is low in hydrocarbons and rich in methanol into contact'with the distillate from said distillation of said oil fraction-inthe presence of p-dioxane.

6. The process for the treatment of an oil iraction containing toluene and a mixture of likeboiling, non-aromatic hydrocarbons which comprises fractlonally distilling said oil fraction in the presence of crotonaldehyde and'thereby taking cil as distillate azeotropes ofsaid like-boiling, non-aromatic hydrocarbons with crotonaldehyde and leaving a residue enriched in toluene. then fractionally distilling said distillate in the presence of methanol and thereby taking off as distillate said like-boiling, non-aromatic lhydrocarbons as azeotropes with-methanolzand leaving crotonaldehyde in a residue of the distillation and returning said residue containing crotonaldehyde to the aioredescribed distillation ofsaid oil fraction in the presence of '7. 'I'he process for the treatment of an oil fraction containing toluene and arnixture. of

like-boiling, non-aromatic hydrocarbons which comprises fractionally distilling said oil fraction in the presence of crotonaldehyde and'thereby taking off as distillate vapors azeotropes of said like-boiling, non-aromatic hydrocarbons with crotonaldehyde and leaving a residue enriched in toluene, then fractionally distilling said distillate vapors 'in the presence of methanol and thereby taking oil? as distillate said like-boiling, non-aromatic hydrocarbons as azeotropes with methanol and leaving'crotonaldehyde in a resi- .'due .of thedistillation, returning said residue v containing crotonaldehyde in the aforedescribed boiling. non-aromatic-hydrocarbons which comprises `fractionally distilling said oil yfraction in crotonalboiling, non-aromatic hydrocarbonsiwhich comi crotonaldehyde to the aforedescribed distillationA the presence of ethylene glycol methyl ether. thereby taking 01T as distillate azeotropes of said like-boiling, non-aromatic hydrocarbons with ethylene glycol methyl ether and leaving a residue enriched in "xylene, then fractionally distilling said distillate in the presence of'water and thereby taking oil as distillate said like-boiling, nonaromatichydrocarbons as azeotropes with Water 'and leaving ethylene glycol methyl ether in a residue of the distillation and returning said residue containing ethylene glycol methyl ether to the afoiedesciibed distillation of said oil fraction in the presence of ethylenel glycol methyl ether.

9. The process for the treatment of an oil fraction containing xylene andA a mixture of likeboiling, non-aromatic hydrocrbons which comprises fractionally distilling said oil fraction in the presence of ethylene glycol methyl ether, thereby taking off as distillate azeotropes of said like-boiling, non-aromatic hydrocarbons `withI ethylene glycol methyl etherV and leaving a resiy due enriched in Xylene, then fractionally distilling said distillate in the presence ofl water and thereby taking oil as distillate said like-boiling, non-aromatic hydrocarbons as azeotropes with water and leaving ethylene glycol methyl ether in a residue of the. distillation, returning said residue containing ethylene glycol methyl ether to the aforedescribed distillation of said oil fraction in the presence of ethylene glycol methyl ether, cooling the distillate containing'said like-boiling,

non-aromatic hydrocarbons as azeotropes with water and thereby separating the distillate linto two liquid phases and returning the liquid phase thus obtained which is low in hydrocarbons and rich in water into contact with the distillate from said distillation of said oil fraction in the presence of ethylene glycol methyl ether. v l

iu. ,The process for the treatment of an oil fraction containing toluene and a mixture of likeprises fractionally distilling said oil fraction in the presence of crotonaldehyde and thereby taking oft as distillate azeotropes of said like-boiling,v non-aromatic hydrocarbons with crotonaldehyde,

and leaving a residue enriched in toluene, then fractionally distilling said distillate in the presence-of aqueous ethanol and thereby taking oli as distillate said like-boiling, non-aromatic hydrocarbons as aze'otropes with ethanol andwaterk and leaving crotonaldehyde in a residue 'of the distillation, returning said residue containing of said oil fraction in the presence of crotonaldehyde, cooling the distillate containingL said likeboiling, non-aromatic hydrocarbons as azeotropes with ethanol and water and thereby separating the distillate into two liquid phases and .returning the liquid phase thusjobtained which is low in hydrocarbons and rich'in aqueous ethanol f into contact with the distillate from'said distillation of'said oil fraction in the presence ofy crotonaldehyde. 'f

11. vThe process for the treatment Y of an oil fraction containing a volatile, aromatic hydrocarbon and a mixture of like-boiling, non-aromatic hydrocarbons .which comprisesvaporizing said like-boiling, non-aromatic. hydrocarbons of said oil fraction and rectifying the vapors-in a rectication column by passing them upward ilrst through a vzone in which they contact a liquid reflux containing hydrocarbons of said oil fraction and an azeotropic agent B then through a zone'i'n 'which they contact a liquid reflux contain'ing hydrocarbons of said-oil fractionandan -but vapors of said like-boiling, non-aromatic hyr drocarbons entering said second zone pass therethrough and with vapors of agent A are withdrawn from said rectification column, said agents Y being `materials which form low-boiling yazeotropes with said like-boiling, non-aromatic hydrocarbons, agent A forming azeotropes therewith which have lower4 boiling points than the azeotropes of agent B therewith, andagent B being a material which (l) is more effective than agent A for separating from the aromatic hydrocarbon the like-boiling, non-aromatic hydrocarbons of said oil fraction, (2) is less readily separable than agent A from its azeotropes with said non-aromatic hydrocarbons, and (3) agent B and any azeotropes it may form with agent A alone and with A together with hydrocarbons in said oil fraction have higher boiling points than agent- A and the azeotropes of A with the hydrocarbons'in said oil fraction, whereby liquid is withdrawn from the bottom of said rst zone'enriched in said aromatic and substantially free of agents A and B, a distillate is produced containing said like-boiling, non-aromatic hydrocarbons and agent A, and agent B is largely retained in the rectiiication column. q

l2. The process for the recovery of a volatile, aromatic hydrocarbon trom an oil fraction con, taining the same and a mixture of like-boiling. non-aromaticv hydrocarbons which comprises continuously introducing said oil fraction into a continuously operable fractional distillation column in which the oil fraction passes downwardly in the column, is heated to vaporize constituents of the oil fraction and the vapors thus generated pass upwardly in the column in contact' with a liquid reflux containing hydrocarbons of said oil fraction, maintaining in the liquid reilux in a lower zone in said column an azeotropic agent B, in said lower zone heating said liquid reiiux to a temperature at which thev liquid reflux leaving the bottom bf said'zone is substantially free of agent B, maintaining in an upper zone in said columnan azeotropic agent A, and maintaining at a point in said column above the point of introducing said oil fraction thereto a temperature below the boiling point of the azeotropes of agent B and said like-boiling, non-aromatic hydrocarbons but high enough for vapors of azeotropes of agent A and said like-boiling, non-aromatic hydrocarbons to be carried out of the top of said column, said agents being materials which form low boiling azeotropes with said like-boiling, non-aromatic hydrocarbons, agent A forming azeotropes there'zwith which have lower boiling points than the'azeotropes or agent B therewith. and agent B being a material which (l) is morev eilective than agent A for separating from the aromatic hydrocarbon thev like-boiling, non-aromatic hydrocarbons of saidloil fraction, (2) is less readily separable than agent Afrom its'azeotropes with said vnon-aromatic hydrocarbons and (3) agent B and any azeotropes it may form with agent A alone and'with A together with lhydrocarbons in said oil fraction have higher boiling points than agent A and lthe azeotropes o! A with the hydrocarbons in said oil fraction, wherebysaid aromatic hydrocarbon in the oil fraction fed into said column passes downy from an oil fraction containing the same and a mixture of like-boiling, non-aromatic hydrocarbons which comprises continuously introducing said oil fraction into a continuously operable fr-ational distillation column in which the oil fraction passes downwardly in the column, is-

heated to vaporize constituents of the oil fraction and the vapors thus generated pass upwardly in the column in contact with a liquid reux containing hydrocarbons of said oil fraction, maintaining p-dioxane in the liquid reilux in a lower zone in said column, in said lower zone heating said liquid reflux to a temperature at which the liquid reux leaving the bottom of said zone is substantially free of said p-dioxane, maintaining in an upper zone in said column methanol, and maintaining Aat a point in said columnabove the point of, introducing said oil fraction thereto a temperature below the boiling point of the azeotropes of p-dioxane and said like-boiling, non-aromatic hydrocarbons but high enough for vapors of azeotropes of the methanol and said like-boiling non-aromatic hydrocarbons to be carried out of the top of said column, whereby toluene in the oil fraction fed into said column passes downwardly in the column into fraction containing a volatile, aromatic hydrocarbon and a mixture of like-boiling, non-aromatic hydrocarbons which comprises vaporizingsaid like-boiling, non-aromatic hydrocarbonsfof said oil fraction and rectifying the vapors in a rectication column by passing them upward iirst through a zone in which they contact a liquid reilux containing hydrocarbons of said oil fraction and an azeotropic agent B, then through a. zone in which they contact a liquid reflux con; taining hydrocarbons of said-oil fraction and anazeotropic agent A, in said iirst zone heating said liquid reiiux to a temperature at which agent B is vaporized therefrom and reiiux liquid leaving the bottom of said zone is substantially free of agent B, in said second zone cooling the vapors to a temperature at which the vapor of agent B passing upward from said first zone is condensed and iiows downwardlyl into said iirst zone but vapors of said like-boiling, non-aromatic hydrocarbons entering said second zone .pass therethrough and with vapors of agent A are withdrawn from said rectification column, said agents being polar organic compounds havinga boiling point such that they form lower-boiling azeotropes with said like-boiling, non-aromatic hydrocarbons, agent A forming azeotropes therewith which have lower boiling points than Athe azeotropes of agent B therewith, and agent B being a material which (1) is more eiective than agent A for separating from the aromatic hydrocarbon the like-boiling, non-aromatic hydrocarbons of said oil fraction, (2) is less readily separable than agent A from its azeotropes with said non-aromatic hydrocarbons, and (3) agent 14. The process for the treatment of an oil- 2,376,870 B and any azeotropes it may form with agent A alone and with A together with hydrocarbons in said oil fraction have higher boiling points than agent A and the azeotropes of A with the hydrocarbons in said oil fraction, whereby liquid is withdrawn from the bottom of said nrst zone enriched in said aromatic and substantially free ofagents A and B, a distillate is produced containing said like-boiling, non-aromatic hydrocarbons and agent A, and agent B is largely retained in the rectication column. y

15. 'I'he process for the treatment of an roil fraction containing a volatile aromatic hydrocar- K bon and a mixture of like-boiling, non-aromatic hydrocarbons which comprises distilling said oil fraction and rectifying the distilled oil vapors in the presence of an azeotropic agent B and thereby taking off as 'distillate azeotropes of said likeboiling, non-aromatic hydrocarbons with agent B and leaving a residue enriched in said aromatic hydrocarbon, rectifying vapors of said azeotropes in the presence of an azeotropic agent A and thereby taking ofi' as distillate said likeboiling, non-aromatic hydrocarbons as azeotropes with agent A and leaving agent B separated from said hydrocarbons, both of said' agents being materials which form low boiling azeotropesv with said like-boiling, non-aromatic hydrocarbons, said agent A further forming with `said like-boiling1 non-aromatic hydrocarbons azeotropes having lower boiling points than the azeotropes of agent B with said like-boiling, nonaromatic hydrocarbons and forming with the hygether with hydrocarbons in said oil fraction have higher boiling points than agent ,A and the azeotropes4 of A with the hydrocarbons in said oil fraction.

KARL HENRY ENGEL. 

